LUXEMBOURG/BRUSSELS (Reuters) - Ryanair lost an EU court battle on Thursday in which the airline had sought to continue forcing cabin crew based outside Ireland to take their disputes to Irish courts, in a case with implications across the low-cost airline sector.

The European Court of Justice in Luxembourg ruled in favour of cabin crew based at the Irish carrier's Charleroi airport base in Belgium on the question of which court should decide on their complaint. The employees took the airline to a local court, believing Belgian law would be more favourable to them.

Ryanair argued that Irish courts had jurisdiction over their Irish contracts. But a Belgian court in Mons had requested the ECJ's ruling on whether its own judges had jurisdiction.

"The Court (of Justice) points out first of all that, as regards disputes related to employment contracts, the European rules concerning jurisdiction are aimed at protecting the weaker party," the Luxembourg-based ECJ said in a statement.

"Those rules enable inter alia an employee to sue his employer before the courts which he regards as closest to this interests," it said.

Ryanair said it welcomed the ruling for recognising that the home base of the employee should not be the sole determinant of what court can hear disputes on labour issues.

"Maintaining broad assessment criteria ensures that the most appropriate jurisdiction should apply in cases involving international transport workers rather than a sole criterion approach, which would narrow the assessment and restrict movement and flexibility with a myriad of regulations and different crews throughout Europe," Ryanair Chief People Officer Eddie Wilson said.

"We do not believe this "Mons" ruling will in any way alter our Irish contracts of employment or the union rights which all of our people enjoy under the protection of the Irish Constitution."

Low-cost carriers such as Ryanair and easyJet have bases all over Europe, including in France, Spain, Italy and Germany, where both planes and crews are stationed.

This means crews can return to their home base each night, allowing the airlines to avoid costs involved with overnight rest stops.

The crew involved in the case had employment contracts drawn up under Irish law which said their work was to be regarded as being carried out in Ireland since they were working on Irish-registered aircraft.

But Charleroi airport in southern Belgium was designated as their base, meaning they started and ended their working days there and had to reside within an hour of that airport.

The Court also said that the place where the aircraft aboard which the crew carry out their work are stationed should also be taken into account when determining which court has jurisdiction.

German union Verdi, which represents cabin crew and pilots, welcomed the ruling, saying it meant that the rules in countries in which staff were based would apply and that German labour law can no longer be avoided.

"This is a good day for Europe's passenger aviation industry and its employees. It's a first step in making sure all airlines have to follow the same rights and obligations," Verdi board member Christine Behle said in a statement.

Ryanair said that Ireland had adopted all EU rules on employment rights and in some cases offered better protection that other EU countries.